Strengthening Metallic Structures
A large number of metallic structures in civil engineering (such as road and railway bridges, offshore structures, pipelines, wind turbines, communication towers and mining equipment), aerospace and mechanical engineering (such as aircrafts, ships, trams and trains) are aging. Most of these structures are subjected to cyclic loading. It is estimated that fatigue contributes in about 90% of all service failures in metallic components. The increasing service loads and harsh environmental conditions make these structures even more vulnerable.
Advanced materials such as carbon fibre-reinforced polymer (CFRP), shape memory alloy (SMA) and etc. can be used to increase the sustainability of metallic structures. The CFRP materials are composites with high strength to weight ratio, non-corrosive with a superior fatigue performance. It has been shown that the CFRP material can enhance the fatigue behavior, buckling strength, stiffness and ultimate-load capacity of metallic members. Furthermore, SMAs are intelligent metals that have the capability to recover their shape after a permanent deformation at room temperature followed by a subsequent heating and cooling. It has been shown that SMAs can substantially increase the fatigue/service life of metallic members.
An updated list of recent publications in this Research Topic can be found here on Google-Scholar and Researchgate. A number of pictures and videos related to CFRP strengthening of different bridges can be found in Video/Photo Gallery
Fatigue Strengthening of Riveted Girders of Münchenstein Railway Bridges (in Switzerland) using Pre-stressed CFRP
An innovative pre-stressed un-bonded retrofit (PUR) system was developed and used for strengthening of different metallic bridges. The advantages of the developed PUR system are:
- applicable to unsmooth (e.g., riveted or corroded) surfaces
- fast on-site installation (i.e., no glue and surface preparation)
- no damage on metallic member (no weld, hole or grinding) and adjustable CFRP pre-stress level.
- adjustable pre-stressing level in CFRP.
The system can be easily disassembled/removed from the girders, without any residual effect on the original structure. This makes the system suitable to be used as a temporary or permanent retrofit solution, particularly, for historical bridges (see more info here).
The trapezoidal PUR (TPUR) system was used for fatigue strengthening of riveted girders of Münchenstein Railway Bridge near Basel in Switzerland (see more details here), as shown in Figures 1.a and 1.b
Involved staff: Elyas Ghafoori, Masoud Motavalli
Swiss Federal Railways (SBB)
S&P Clever Reinforcement Company, Switzerland
ETH Zurich and EPFL, Lausanne
Prestressed FRP-Strengthening and Wireless Long-term Monitoring of a Metallic Bridge in Melbourne
A flat PUR (FPUR) system was developed and used for flexural and fatigue strengthening of steel girders of the Diamond-Creek Roadway Bridge in Melbourne in Australia, as shown in Figure 2.a. A wireless sensor network (WSN) system was used for long-term monitoring of the behavior of both of the bridges after strengthening, as shown in Figure 2.b. The WSN system provides the measurement results online for at least one year.
There are several ongoing studies are on CFRP strengthening of steel plates and girders as well as bridge connections.
Involved staff: Ardalan Hosseini, Elyas Ghafoori
Monash University, Australia
Swinburne University, Australia
S&P Clever Reinforcement Company, Switzerland
Victorian Road Authority (VicRoads), Australia
Characterization and Application of a Smart Material for Strengthening of Metallic Structures
Iron-based SMA (Fe-SMA) materials are used for prestressed strengthening of metallic members (see Fig. 3). Fe-SMA has considerable recovery stress and a good fatigue life. More details about the characterization and cyclic behavior of the Fe-SMA material can be found in here.
Through an extensive test program, it was shown that pre-stressed/activated Fe-SMA can substantially enhance the fatigue life of steel members, and in some cases, result in a complete fatigue crack arrest (see more details here).
There are several ongoing studies are on Fe-SMA strengthening of steel plates and girders as well as bridge connections.
Involved staff: Mohammadreza Izadi, Elyas Ghafoori
re-fer AG, Switzerland and University of Tehran
Strengthening of aircraft metallic members using a smart "shape memory" patch
Damage tolerance (DT) design philosophy is often used in the safety critical aerospace sector to ensure the structural integrity. A general definition of DT is the ability of structure to sustain predicted loads in the presence of fatigue, corrosion or accidental damage until such damage is detected, through inspections or malfunctions, and retrofitted. Repair of fatigue cracked aircraft structures is therefore indispensable. Especially, operators of both civil and military aircraft currently suffer from the aging problem of aircraft that comprises mainly metallic structures. In this project, an advanced smart repairing (fatigue strengthening) system for aging metallic aircraft structures using novel shape memory alloys (SMAs) is proposed and tested (see Fig. 4).
Involved staff: Wandong Wang, Elyas Ghafoori
• re-fer AG, Switzerland
• Australian Defence Department, Melbourne